1. Technical Field
The invention relates to an apparatus and method for continuously delivering and non-intermittently introducing a liquid into a main flow.
2. Background Information
Gas turbines are nowadays designed so as to be optimized in terms of both output and efficiency. Today's gas turbines therefore can have very small power reserves over and above the rated output. In order to briefly increase the output, or increase it for a longer period, above the rated output of the gas turbine, water or another suitable liquid can be injected or sprayed into the compressor flow of a gas turbine. The increase in output achieved as a result is due to the fact that the liquid evaporates after the spraying and heat is thereby extracted from the air flowing through the compressor. This evaporation process taking place continuously constitutes, as it were, continuous intercooling of the compressor flow, the result of which is that less compressor work has to be applied for compressing the compressor flow to a preset pressure ratio than would be required without the introduction of water. At the same time, the air mass flow rate through the compressor is increased. At a constant combustion-chamber outlet temperature, a higher net output is therefore available, which is used, for example, as shaft output. Such injection of water has been disclosed, for example, by the publications DE 25 49 790 and FR 1 563 749, which are hereby incorporated by reference in their entireties.
It is known to introduce water or another suitable liquid, in particular mixtures of water and additives, for example water/alcohol mixtures, upstream of the compressor or between two compressor blade rows. In the case of the spraying upstream of the compressor, the spraying arrangement is located upstream of the first compressor stage.
For reasons of simplicity and efficiency, in addition to atomizer nozzles assisted by auxiliary media, e.g. air-assisted atomizing nozzles, “airblast atomizers”, pressure atomizer nozzles are often used for spraying water. During pressure atomization, the atomizing supply pressure can be kept approximately constant or varied only within narrow limits, since this can influence the droplet spectrum to a considerable extent. In order to vary the sprayed mass flow, nozzle groups are frequently switched on or off in this case. However, the abruptly changed setpoint mass flow can be provided by a pump or another delivery device only with a time delay. This is schematically illustrated in FIG. 1: if liquid is additionally admitted to a number of atomizer nozzles, a setpoint characteristic according to the curve identified by 2 results, assuming a uniform atomizing supply pressure. On account of the inertia of the pump, however, an actual characteristic according to 1 is obtained. This results in a temporary collapse of the atomizing supply pressure and a period in which droplets which are too large are produced.
A completely analogous situation occurs if a very rapid output gradient of the gas turboset is to be produced by an increased injection quantity, such as in frequency backup operation for example. In this case, the mass flow is increased more slowly than according to the setpoint selection, from which a delayed increase in output results. These problems equally occur when using pressure atomizer nozzles and atomizers assisted by auxiliary media.